From lampreys to salamanders: evolving neural controllers for swimming and walking

FromlampreystosalamandersevolvingneuralcontrollersforswimmingandwalkingAukeJanIjsp eertJohnHallamDavidWillshawDeptof Articial Intelligence U ofEdinburghForrest Hill EdinburghEHQ UKfaukei johngdaiedacukCentreforCognitive ScienceUof EdinburghBuccleuchPlace EdinburghEHLWUKdavidcnsedacukAbstractThis pap er presents how neural swimming controllersfor a lamprey can b e adapted for controlling b oth theswimmingandthewalkingofasalamanderlikeanimatUsingaGeneticAlgorithmGAweextendaconnectionistmo delofthebiologicalCentralPattern Generator CPG controlling the swimming of alamprey Ekeb erg to control the lo comotion ofa D mechanical simulation of a salamanderWerstsummarizeexp erimentsontheevolutionofalternativeswimmingcontrollersforthelampreyIjsp eertet alTheaimofthatworkastostudy whether there exists other neural congurationsthanthatfoundin thelampreywhichcouldcontrolswimmingwiththesamee ciencyandtodevelopametho dfordevelopingneurallo comotioncontrollers using a GA We then presenthow that metho dnamelyastagedevolutionoftheneuralconguration of a connectionist mo del can b e used to extendswimming controllerstocontrol b oth swimming andwalking Controllers which similarly to CPGs of animals canpro duce complex oscillationswhen receivingsimple excitatory signals are thus develop ed In particular we generate a controller which can switch fromswimming to walking and pro duce dierent sp eeds ofmotion dep ending on its excitationIntro ductionAlthoughthereexistsavarietyofdierentlo comotormovements among vertebrates their control systems appearrelativelysimilaracrossdierentsp ecies Grillneret al Lo comotion is controlled by networks of interneurons lo cated in the spinal cord which pro duce thecomplex patterns of oscillations necessary for motion Asdemonstrated in the s byOrlovsky s classical exp eriment on the cat as rep orted in Grillner thesenetworks called Central Pattern Generators needonlysimple excitatory signals from the brain to pro duce theco ordinated oscillations necessary for motionOur research fo cusses on biologically inspired neurallo comotion controllers for autonomous agents and howtodevelop them using a GeneticAlgorithm GA In particular we are interested in which kinds of neural conguration can control the anguiliform swimming observedin lampreys and the swimming and walking of salamanders Both lampreys and salamanders pro ject themselvesin water by undulation of the b o dy without use of nsor limbs The undulation is a traveling wae propagatingfromheadtotailWhenthesalamander switchesswimmingtowalking itstrunkceases topropagate anundulation and instead p erforms an S shap ed standingwave with theno des atthe level ofthe girdles Frolichand Biewener The b ending of the trunk helps thesalamander to increase thereach of its limbs which areattached laterally to the trunkThe work presented here follows exp eriments in whichwe used a GAtoevolve swimming controllers for a simulatedlampreywithalternativeneuralcongurationstotheobservedbiological conguration Ijsp eertet al The work was inspired by a biological connectionistmo delofthelamprey sCPGEkeb erg Wedevelop ed articial controllers using an incremental approach whereincreasingly complexcontrol mechanismsare develop ed using elements of theprevious evolutionarystageHereasthemetho dprovedtobeausefuldesigntechniqueweapplyitagaintostudywhethercontrollersforswimmingcanbeextendedtotrolb oth swimming and walking of a salamanderlike animatWalking controllers based on oscillatory networks of theswimming controllers are generated for the control of adimensional mechanical simulation of the salamanderWeare interested in the development of control mechanismswhichsimilarlytotheCPGsofanimalscanpro ducecomplexoscillationswhenreceivingsimpleinputsignals Ap otentialapplication ofthese controllerscould b e the control of lo comotion of an amphibian rob ot Another motivation is to gain some insights on howCPGs function in real animals Note that the evolutionfrom swimming to walking controllers and its applicationto rob otics has b een studied b efore Lewis but at